How to generate <sensor_msgs::PointCloud2> format bagfile

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Yes, thank you very much for your advice. Here is my current operation process：

roscore
rosrun velodyne_driver velodyne_node _model:=VLP16 _pcap:=my.pcap _read_once:=true
rosrun nodelet nodelet standalone velodyne_pointcloud/CloudNodelet _calibration:=VLP-16.yaml

Then began to run my program, now I can finally see the images in the rviz. And I have a new problem, I want to save the data of PointCloud2. After executing the above three steps, I run the following command in a new terminal：

rosrun rosbag record -O out1.bag /velodyne_points

Terminal print

[ WARN] [1565691355.513475857]: /use_sim_time set to true and no clock published.  Still waiting for valid time...

How can I solve this problem. Once again thank you. : )

Im glad it helped. In addition, it is a common practice that if you have a new problem you should create a new question to keep problem tracking organized. As for your new problem, refer to this question. As you can see you can set the /use_sim_time parameter to true/false like this:

rosparam set use_sim_time true

thank you very much